This invention generally relates to apparatus and methods for obtaining samples for analysis and more particularly relates to an apparatus and method for removing a wall portion from a wall of a tubular member, such as a nuclear steam generator tube, so that the tubing material thereof may be analyzed.
It is well known that a typical nuclear steam generator or heat exchanger generates steam when heat is transferred from a heated and radioactive primary fluid to a non-radioactive secondary fluid of lower temperature. In order to accomplish the heat transfer, the secondary fluid surrounds a plurality of leak-tight heat transfer tubes disposed in the steam generator as the primary fluid flows through the tubes.
Occasionally, however, the steam generator tubes may experience tube wall cracking and thus may not remain leak-tight. If through-wall cracking occurs, the radioactive primary fluid may leak through the cracks and commingle with the nonradioactive secondary fluid, a highly undesirable result. Therefore, the tubing material is periodically sampled and analyzed in order to determine whether tube wall cracking is eminent.
One prior art method of obtaining the necessary samples is to "pull" or extract one or more of the tubes in order perform analyses thereon. The tube "pull" process includes heating the tube to relax the tube, cutting away a section of the tube from the inside thereof, pulling the severed tube section through the tubesheet hole as segments of the severed tube section are progressively cutting-off, and installing a plug in the now empty tubesheet hole formally occupied by the tube. This process may be repeated for each leg of the U-shaped tube.
However, applicants have observed that the tube pull process is time consuming because it requires up to approximately 24 hours per tube to complete. Thus, the time required to perform the tube pull process may undesirably extend plant outages and may increase radiation exposure to service personnel performing the "tube pull". It is important to avoid an extended plant outage because such an extended outage may result in approximately $300,000 per day in replacement power costs to the reactor owner. Also, it is important to avoid increased radiation exposure to service personnel because U.S. Government regulations require radiation exposure be held to a level that is as low as reasonably achievable.
Hence, there has been a long felt need in the industry to provide an apparatus and method for sampling the tubes that is not time consuming, does not result in extended plant outages and does not increase radiation exposure to service personnel. Therefore, such an apparatus and method preferably should be capable of sampling the tube without the time-consuming need to "pull" the tube.
Therefore, what is needed are an apparatus and method for removing a wall portion from a wall of a tubular member, such as a nuclear steam generator heat transfer tube, so that the tubing material thereof may be analyzed.